The invention relates to a method for estimating the position of a subscriber station of a radio communication system and a corresponding network device.
Localizing subscriber stations in cellular networks has become increasingly important in the past few years. On the one hand, there are regulations in some countries, whereby the operating companies are bound by law to determine the location of emergency calls. On the other hand, there is a commercializing of location-associated services at present, which requires a simple and cost-effective localizing of subscriber stations. There is a plurality of technical solutions in order to estimate the position of a subscriber station, the accuracy of which and the cost of which vary. For example, the position of a subscriber station can be determined with the help of an EOTD (Enhanced Observed Time Difference) method, by the UTDOA (Uplink Time Difference of Arrival) or the AGPS (Assisted GPS). Either the installation of additional components in the radio access network or the use of special subscriber stations is required for this purpose.
On the one hand, many operating companies are not willing to make such investments while, on the other hand, many applications do not require a very accurate determination of the position. That is why localizing methods are particularly in demand, said methods being cost-effective and able to locate a subscriber station with an acceptable level of accuracy. However, the use of cell identification (cell ID) is not sufficient for this purpose. Only the inclusion of information in addition to the cell identification permits the positioning of subscriber stations with an accuracy which is sufficient for most applications. One option for making available additional information is represented by the evaluation of the signal strengths of signals received from a subscriber station. As a rule, the signal strengths of receive signals are used by the transmitting station, which provides coverage for a radio cell in which the subscriber station is located and by additional radio cells adjacent to the transmitting stations. For example, in GSM systems (GSM: Global System for Mobile Communications) each active mobile station reports every 480 ms about the signal strength of receive signals of the base station covering them and about the signal strengths of additional receive signals of up to six adjacent base stations. These reports are compared with a signal strength database in order in this way to estimate the most likely location of the subscriber station in combination with the cell identification, if required.
Such methods and systems are for example known from the international patent application WO 98/15149.
Previously known methods for estimating the position of subscriber stations produce good results for estimating the position especially if a plurality of reports of a subscriber station about signal strengths of receive signals is used at the same time for estimating the position. However, in a GSM system for example, when for example 10 reports about the signal strengths of receive signals are used, there is an additional delay of approximately five seconds when determining the positions of a subscriber station.
From DE 100 56 22 A1, a method is known for localizing the traffic in a cellular mobile telephony network, in which from the transition probabilities of a hidden Markov model and the observation probabilities of an interference model from a sequence of reports, a highly probable path of a mobile subscriber can be determined. The reports contain the field strength values of base stations measured by the mobile subscriber. The reports are either sent directly to an arithmetic unit by the mobile subscriber or first collected by a base station and, if required, supplemented by additional measured values and sent in the form of one complete message to the arithmetic unit.